a) Field of the Invention
The invention relates to a steering column for a motor vehicle which is displaceable in at least its longitudinal direction, comprising a support unit connectable with the chassis of the motor vehicle, a setting unit and a clamping mechanism. In the opened state of the clamping mechanism, the setting unit is at least displaceable with respect to the support unit in the longitudinal direction of the steering column, and in the closed state of the clamping mechanism the set position of the setting unit is secured in position with respect to the support unit. The clamping mechanism comprises a clamp bolt and at least one arrest element cooperating with at least one securement element. At least one arrest element during the closing of the clamping mechanism is displaced in the axial direction of the clamp bolt with respect to the support unit and is clamped with a securement element connected with the setting unit, and at least one securement element is connected with the setting unit so that during normal operation it is held nondisplaceable with respect to the setting unit in the longitudinal direction of the steering column and, in the event of a crash, is dislocatable with respect to the setting unit with the absorption of energy.
b) Description of Related Prior Art
Adjustable steering columns serving for the adaptation of the position of the steering wheel to the seating position of the driver are known in various embodiments. Apart from adjustable steering columns which are only adjustable in length or height and inclination direction, respectively, steering columns are known which are adjustable in length as well as also height and inclination direction, respectively.
Adjustable steering columns, in which the set position is fixed by means of a clamping mechanism, in which the clamping mechanism holds securement elements in engagement with one another, and in which elements cooperate under frictional and/or positive locking, are disclosed, for example, in EP 0 802 104 B1, EP 0 836 981 B1, U.S. Pat. No. 5,722,299 A or EP 1 382 509 A1. In the case of the adjustable steering column of EP 0 802 104 B1, in the closed state of the clamping mechanism, (lamella) disk packs are tightened with one another, and one of the disk packs is disposed on the setting unit or jacket unit and the other on the support unit. In the case of the device of EP 0 836 981 B1, in the closed state of the clamping unit toothings are brought into engagement with one another, which block a dislocation of the steering column. The support unit herein comprises only one shank on one side of the setting unit, and the setting unit is tightened against the shank in the closed state of the clamping mechanism. U.S. Pat. No. 5,722,299 A also discloses, in particular in the embodiment examples according to FIGS. 28 to 39, a clamping mechanism in which securement elements cooperate via toothings under positive locking. The support unit comprises side jaws located on both sides of the setting unit, and the jaws penetrate through openings by the clamp bolt of the clamping mechanism. In the steering column of EP 1 382 509 A1, snap bolts and bores are provided as cooperating securement elements into which the snap bolts can engage.
It is further known to connect the steering column of a motor vehicle via energy-consuming means with the chassis of the motor vehicle. Conventionally in adjustable steering columns the support unit, in a manner consuming energy, is connected displaceably with a chassis part disposed on the chassis of the motor vehicle. Such a design is shown, for example, in U.S. Pat. No. 5,517,877 A. In non-adjustable steering columns, the jacket tube itself is connected such that it consumes energy, with the chassis of the motor vehicle as is shown, for example, in U.S. Pat. No. 5,082,311 A. The energy-absorbing device in this steering column is formed by holding brackets disposed on the jacket tube, which have elongated holes extending in the longitudinal direction of the jacket tube. The elongated holes are penetrated by a bolt which extends further through a bore in a chassis-stationary part. In the event of a crash, the jacket tube, together with the holding brackets disposed on the jacket tube, is displaced with respect to the bolts, wherein these [bolts] widen the elongated holes with the absorption of kinetic energy of the jacket tube.
A steering column of the type described in the introduction is further disclosed in EP 0 849 141 A1. On the jacket tube are secured mounting flanges which delimit a slot extending in the longitudinal direction of the jacket tube. A securement element for the securement of the longitudinal displacement of the steering column is guided between these mounting flanges such that it is displaceable in the longitudinal direction of the steering column. A clamp bolt penetrates through an opening in a side shank, disposed on one side of the jacket tube, of a chassis-stationary support unit and an elongated hole in the securement element extending in the longitudinal direction of the steering column. In its closed state, a clamping mechanism fixes the set position of the steering column. The clamping mechanism clamps the side face of the securement element facing the side shank of the support unit with the side face of the side shank facing this securement element, of the support unit which, consequently, forms a further securement element for securing in position the longitudinal adjustment of the steering column. Furthermore, the L-shaped mounting flanges disposed on the jacket tube in the closed state of the clamping mechanism are clamped through the clamping force exerted by the clamping mechanism additionally into slots of the securement element guided on the mounting flanges such that it is displaceable in the longitudinal direction. In the event of a crash, the securement element can be displaced with respect to the mounting flanges while overcoming the friction in effect between these parts. Although this design permits a compact structure, this device, inter alia, has a disadvantage in that the extent of the energy absorption between the mounting flanges of the jacket tube and the securement element depends on the clamping force of the clamping mechanism. This clamping force can change over the course of time. The development of a predetermined force-path diagram for the energy absorption of the crash energy is not possible in a satisfactory manner.